If you were ever curious about IoC, the Dependency class is only about 100 lines of code. You can even skip the dynamic operations and it's only ~50 lines of code. The dynamic operations then just use reflection to invoke the typed operations.

Dependency uses static generic fields, so resolution is pretty much just a field access + invoking a delegate. The reason for this speed and simplicity is that it's very light on features, like lifetime management, instance sharing, etc. It's really just the core for dependency injection.

Still, it gets you far because the constructor delegate is entirely user-specified. You can actually build features like lifetime management on top of this core by supplying an appropriate delegate to Register<T>.

This container doesn't handle cleanup though, so the thread-local example depends on the client to properly dispose of the thread-local IFoo instance. AutoFac IoC claims to handle disposal of all disposable instances, so I'm reading up a little on how that's done.

This approach seems to handle most common scenarios, but there are no doubt some limitations. Still, it's a good introduction for those curious about IoC implementation.